1. Field of the Invention
The present invention relates to medical devices that transmit laser energy. Specifically, the present invention relates to fiber optic laser energy delivery devices that emit a laser beam substantially laterally relative to the longitudinal axis of the fiber optic in a liquid medium.
2. Description of the Prior Art
In conventional laser energy delivery devices, a laser beam is emitted from the distal end of one or more optical fibers toward the point of application in the human body. Medical applications of lasers, such as in urology, gynecology, general surgery, orthopedics, ophthalmology and other surgical procedures, sometimes require laser energy to be emitted laterally from the axis of the optical fiber, so that, in urological applications for example, the lateral lobes of the prostate may undergo ablation and/or coagulation to create an enlarged region or passage for an enhanced fluid flow.
A prism can be used to laterally reflect light energy, so long as the index of refraction of the medium surrounding the reflective surface of the prism is substantially lower than the index of refraction of the prism itself, provided the reflective surface of the prism is at or below the critical angle for total internal reflection. This critical angle depends on the ratio of the respective refractive indices between the material of the prism and that of the environment or adjoining substance immediately outside the prism's reflective surface (i.e., the boundary interface). In order to achieve total internal reflection, for a given lateral reflection angle, a substance such as air (with a refractive index of about 1) can be used to assure a sufficiently low refractive index relative to that of a glass prism (refractive index 1.46). As a result, glass prisms function properly in an air environment. However, in water (refractive index 1.33) or in saline (refractive index about 1.33, depending on concentration), glass prisms do not effectively reflect light energy laterally substantially close to 90 degrees because the difference in refractive indices between the glass and the ambient medium is not great enough.
Moreover, surrounding the prism with air has disadvantages. One such disadvantage is that an enclosure transparent to the wavelength of energy being used, such as a glass encapsulating sleeve, is needed to contain and maintain an air environment at the prism interface. This, in turn, requires that the prism be positioned in precise orientation within the sleeve. To achieve this, a very tedious alignment procedure, difficult to accurately replicate in production, is involved. On the other hand, if the prism is not in precise alignment, internal reflection may not be achieved, or a laser beam in an errant direction may be emitted. Affixation of the glass encapsulating sleeve to the buffer coating or cladding of an optical fiber in an airtight manner is also difficult to assure in production.
Another problem with a glass sleeve is that an output power loss of five to ten percent may be experienced due to scattering and back reflection from the sleeve. This is a significant and undesirable power loss.
In surgical devices that come in contact with tissue it is also difficult to maintain the glass encapsulating sleeve at a sufficiently low temperature to prevent tissue from sticking thereto. If this happens, the temperature of the sleeve can quickly rise to the point of destruction, with the potential for leaving fragments of the glass sleeve in the body, which might necessitate surgery to remove them.
Still another problem with the glass encapsulating sleeve is that it is fragile. Physical stresses exerted during insertion through endoscopes or guiding catheters, or during the lasing procedure could cause the sleeve to break, leaving glass fragments at the medical procedure site and causing complications to the patient that might require an invasive surgical procedure to correct.
While laser energy may be laterally reflected from a polished metal surface in a fluid medium, some of the laser energy may be absorbed by the metal surface, thereby raising its temperature. If the metal surface is contaminated by tissue or body oils, the temperature of the metal surface can rapidly increase, causing the metal to deteriorate or melt.
Therefore, it would be desirable to have a medical device that reflects the laser energy laterally in a fluid medium without the need for a metal reflecting surface or glass encapsulating sleeve. The present invention provides such a device.